The referenced U.S. Pat. No. 3,949,401 describes radio equipment useful in the field of broadcast traffic information systems including a decoding circuit which checks if a transmitter radiates a particular region identification frequency and further checks for the presence of traffic announcement identification frequencies.
Radio traffic information, on specific frequencies and, preferably, in the FM band, are becoming more widespread. A suitable receiver, as explained in the aforementioned patent, includes a radio signal receiving stage which provides program signals and traffic information signals to an audio stage for, respectively, reproduction thereof. A traffic information decoder is provided responsive to predetermined signals received by the receiving stage to provide traffic information control signals to a transfer circuit connected to transfer to the audio stage either program signals, such as entertainment, news and the like, or traffic information signals. The circuit may, additionally, be used to transfer to an audio stage signals derived from magnetic tape transducers, for example an audio cassette recorder. If it is not desired to utilize the traffic information feature of the receiver, then a switch is provided to disable the traffic information portion.
The receivers to which the present invention relate utilize codes or frequencies to characterize regions characteristic of certain listening areas, within which a specific transmitter can be received, and to characterize the traffic information content, namely that a specific transmitter is not then radiating general program material but, rather, a traffic information. In accordance with the system described in the aforementioned patent, traffic information transmitters, together with program information, additionally radiate a specific transmitter code for all traffic information and, in addition and regionally separate, a further signal which is representative only of the receiving area of the respective transmitter. The signal which is standard for the entire system is radiated only if a traffic information bulletin, or the like, is to be radiated.
The respective signals are decoded in the receiving decoders. Various types of such decoders have been proposed. In one simple type, the general signal type identification is decoded and, in addition thereto, the regional signal. These decoders can readily be tuned to receive, for example in an automobile radio, the respective transmitters which have been assigned the task of radiating traffic information.
Radio receivers which have the traffic information decoding feature frequently include a switch, typically operated as a momentary-contact pushbutton which, when operated and upon transmission of traffic information, will disable transfer of radiated program signals to the receiver, that is, by muting the program signal. To insure that the user will listen to and adequately hear the traffic information transmission, the level of reception is raised, even though the user may have set the receiver at a low level, for example to hear only "background music". If the receiver in a vehicle is a tape recorder - receiver combination, then, additionally, the audio signal from the tape recorder can be interrupted and, if desired, the playback unit can be stopped as well so that, upon receipt of a traffic information, any recording which is being reproduced is interrupted at that point, permitting resumption from the stop point when the traffic information transmission has terminated.
The minimum volume level at the audio amplifier for reproduction of traffic information must be set. This requires that, during installation and testing, the receiver can actually receive a traffic information transmission. This, however, can occur only if there are traffic information signals on the air.
In order to test or demonstrate automobile radios having the traffic information feature during a pause of traffic information signals, it is desirable to be able to set the minimum volume level of the receiver portion for the traffic information independently of transmission of traffic information itself; such traffic information cannot always be predicted since it may occur at random times in accordance with emergencies, metereological conditions or the like. It is also desirable to be able to set a minimum volume level for the audio reproduction already at the factory or at least at the time of installation of a specific radio receiver in an automobile.